Tracing Transactions Across Cryptocurrency LedgersHaaroon Yousaf, George Kappos and Sarah Meiklejohn

University College London

Bitcoin and anonymity

Bitcoin and anonymity

“…privacy can still be maintained by breaking the flow of information … keeping public keys anonymous”

“ if the owner of a key is revealed, linking could reveal other

transactions that belonged to the same owner”

Anonymity defeated

On-chain tracking

USENIX Security 2018 Privacy Enhancing Technologies 2018

Cross-currency tracking?

Cross-currency trading• ShapeShift (Aug ‘14), Changelly (‘13)

• Cross-currency trading service (lightweight exchange)

• Allow users to interchange multiple coins/tokens

• ShapeShift supporting 32 coins (Aug ‘19)

• Changelly supporting 107 coins (Aug ‘19)

Why cross trade?

• Non-custodial (Does not require coins in an account)

• Easy to use

• Potential extra anonymity?

• Single rate charge

How to perform a shift?

1

How to perform a shift?

1

2

User’s destination address

How to perform a shift?

1

2

3

What is cross-chain?

?

Coin A

Coin B?

User

Shifting Service

? Unknown

What is cross-chain?

?

??

Aim to find the link“shift”

?

User

Shifting Service

Unknown

Coin A

Coin B

Our contributions

• Blockchain analysis of transactions moving cross-chain

• Created heuristics analysing user behaviours

• Defined a common relationship heuristic identifying major entities (in

paper)

• Investigated real world scams which made use of cross-chain transactions

(more in paper)

• Analysed how users make use of privacy-coin features

Our contributions

• Blockchain analysis of transactions moving cross-chain

• Created heuristics analysing user behaviours

• Defined a common relationship heuristic identifying major entities (in

paper)

• Investigated real world scams which made use of cross-chain transactions

(more in paper)

• Analysed how users make use of privacy-coin features

How?

0: curIn: “BTC”curOut: ”BCH”amount: 0.51566669timestamp: 1525650476.615

1. Scraped public API for recent transactions

https://shapeshift.io/recenttx

How?

0: curIn: “BTC”curOut: ”BCH”amount: 0.51566669timestamp: 1525650476.615

Currency user sent, Input

Currency user wants, Output

Input currency user sent

1. Scraped public API for recent transactions

How?

0: curIn: “BTC”curOut: ”BCH”amount: 0.51566669timestamp: 1525650476.615

2. Search and find this input transaction

+/- blocks

Exact value

How?

UserShapeShift

2. Search and find this input transaction

How?3. Confirm this is correct via official API + find the output transaction

https://shapeshift.io/txstat/<address>

status: "complete"address: "35EgH9XDA2xHhYmuVVrU8FYvwZdetEjSHs"withdraw: "13JwaysXv433bqAWdkHiPEFKRHKzYXrtgh"incomingCoin: 0.51566669incomingType: "BTC"outgoingCoin: "2.7965838"outgoingType: "BCH"Transaction: "e33779961628f9868cad28c0331a9ccb78f76c90240fc14be1b69075377d82b0"transactionURL: "https://explorer.bitcoin.com/bch/tx/e33779961628f9868cad28c0331a9ccb78f76c90240fc14be1b69075377d82b0"

ShapeShift address

Output transaction

How?

outgoingCoin: "2.7965838"outgoingType: "BCH"Transaction: "e33779961628f9868cad28c0331a9ccb78f76c90240fc14be1b69075377d82b0"transactionURL: "https://explorer.bitcoin.com/bch/tx/e33779961628f9868cad28c0331a9ccb78f76c90240fc14be1b69075377d82b0"

ShapeShift

Output transactionRecipient

3. Confirm this is correct via official API + find the output transaction

How summary

1. Scrape public API for transactions

2. Search and find the input transaction

3. Confirm this is correct via the API and obtain output transaction

Linked cross-chain

?

Coin A

Coin B

User

Shifting Service

? Unknown

Found the link“shift”

Our contributions

• Blockchain analysis of transactions moving cross-chain

• Created heuristics analysing user behaviours

• Defined a common relationship heuristic identifying major entities (in

paper)

• Investigated real world scams which made use of cross-chain transactions

(more in paper)

• Analysed how users make use of privacy-coin features

Results

• Scraped ShapeShift public API ~13 months

• 2.8 million shifts total

• Parsed blockchain data from full nodes

• Top 8 currencies - 2.3 million shifts

Cross-chain activity• Traced 1.3M transactions cross-chain

• Corresponding input and output transactions

76.86

23.14

Worst Case (Bitcoin)

Traced Not traced

90.54

9.46

Best Case (Zcash)

Traced Not traced

U-turn• Two shifts, close proximity in time and value

• Use the same coin or address between shift

• Follows movement of user coins

2nd

shift1st

shift

≈95576

10566

1120

Basic (value & time)

Same Address

Same coins

95576

105661120

2nd

shift1st

shift

≈

Round-trip• Two shifts, close proximity in time and value

• 1st shift value similar to 2nd shift or return to the same input address

• Advantage over U-turn: identity of initiator is known

85057

10490

Regular

Sameaddress

85057 10490

Our contributions

• Blockchain analysis of transactions moving cross-chain

• Created heuristics analysing user behaviours

• Defined a common relationship heuristic identifying major entities (in

paper)

• Investigated real world scams which made use of cross-chain transactions

(more in paper)

• Analysed how users make use of privacy-coin features

Case study: Starscape Capital Scam• Investment firm promised 50% return in cryptocurrency arbitrage fund

• Raised 2000 ETH in January 2018 (2.2M USD)

• Disappeared

• 192 transactions (total) – 109 shifted to Monero (465 ETH)

• 2x Monero addresses that received shifted coins

Our contributions

• Blockchain analysis of transactions moving cross-chain

• Created heuristics analysing user behaviours

• Defined a common relationship heuristic identifying major entities (in

paper)

• Investigated real world scams which made use of cross-chain transactions

(more in paper)

• Analysed how users make use of privacy-coin features

Case study: Anonymity coins• Zcash: Shielded pool, privacy feature that hides values + address

• Dash: Coinjoin, privacy feature that mixes transactions with other users

• Significant total volume from both of these coins however…

Zcash Shielded pool 3,808 transactions

774,380 USD

Pool funds sent to ShapeShift

2,068 transactions

1.2M USD

Coinjoin funds sent to ShapeShift

DashCoinjoin

Case study: Anonymity coins

• …we find usage that does not provide anonymity

• Dash U-turns

• Same coins - 5.6%

• Same address - 64.6%

• Zcash U-turns

• Same coins - 28.7%

• Same address - 54.2%

Our contributions

• Blockchain analysis of transactions moving cross-chain

• Created heuristics analysing user behaviours

• Defined a common relationship heuristic identifying major entities (in

paper)

• Investigated real world scams which made use of cross-chain transactions

(more in paper)

• Analysed how users make use of privacy-coin features

Authors are supported by the EU H2020 TITANIUM project under grant agreement number 740558.

THANK YOUQUESTIONS?